Aboslute clustering effects on electron attachment

Lead Research Organisation: Open University
Department Name: Physical Sciences

Abstract

Electron attachment plays an important role in radiation chemistry, for example in DNA damage and ozone depletion. Detailed understanding and quantification of electron attachment processes in isolated molecules and condensed environments is therefore essential to model radiation effects on the nanoscale. My EPSRC CAF probes electron attachment dynamics and reactive pathways in selected biomolecular clusters, building on recent advances such as the observation of electron driven proton transfer in Watson Crick pairs [Bowen et al. ChemPhysChem 11 (2010) 880]. However, relatively little is known about how clustering modifies the absolute probabilities for electron attachment induced processes. While theoretical calculations by my collaborators Fabrikant and Gorfinkiel [J. Chem. Phys. 136 (2012) 184301] have provided evidence for strong enhancements in specific cluster configurations, absolute experimental data for electron attachment to clusters are extremely rare. This project is centered on developing an original technique to produce neutral mass-selected beams with known target density for electron attachment experiments. The method involves neutralization of mass-selected cluster anions by electron photo-detachment from specific weakly-bound anionic states, with minimal change in stability and hence dissociation. The project will provide a breakthrough in quantifying the effects of the local chemical environment on electron attachment induced processes.

Planned Impact

This project will provide key input data for simulating radiation-induced (bio-) molecular damage and nano-scale dosimetry in aqueous environments with applications in radiotherapy. Despite the fact that dissociative electron attachment has been known to initiate DNA lesions for over 10 years [Sanche and co-workers, Science 287 (2000) 1658], low-energy electron interactions are not included in current radiotherapy treatment planning. Dramatic advances in radiation delivery systems (for example using ions beams and new methods in intensity modulated x-ray radiotherapy) have highlighted the importance of more accurate simulations, while computing power no longer prohibits the practical applications of Monte Carlo methods. Advancing the efficacy of cancer therapy methods is essential in view of the aging populations of many countries. Therefore, the development of optimized radiation track simulations applying the most reliable electron attachment (EA) and dissociative electron attachment (DEA) cross sections available will have real benefits for society. The absolute cross sections for electron interactions with water clusters measured during this project will be integrated into Garcia's simulations (LEPTS, currently based on gas-phase cross sections) as a part of a new strategy to account for the hydrogen-bonded environment. Garcia has strong connections with oncologists who are currently carrying out trials comparing clinical radiotherapy treatment plans with damage distributions derived using LEPTS.

Furthermore, the project will contribute to understanding environmental chemistries. The small neutral and charged water clusters studied in this project are prevalent in the atmosphere. In addition, they can provide model systems to help us understand processes in larger clusters, ice crystals, and droplets. Evidently the diverse phases of water play key roles in atmospheric dynamical processes and simulations of their interactions with low energy electrons (the most abundant secondary products of ionizing radiation) require absolute cross sections. Currently available experimental cross sections for electron attachment to selected water clusters are limited to non-dissociative electron attachment [Dubov and co-workers, JETP letters 86 (2007) 520]. To our knowledge, absolute experimental data is not available for DEA to doped water clusters. Our choices of doped cluster targets (hydrated CF3Cl) are known to play roles in ozone depletion chemistries in polar stratospheric clouds [Tachikawa and co-workers, PCCP 10 (2008) 2200]. While the specific complexes studied in this project may not have a significant presence in these environments, they can impact on the residence time of CF3Cl at lower altitudes and hence in the molecule's transport to polar stratospheric clouds. Enhanced DEA cross sections for CF3Cl in hydrated clusters can therefore have significant implications for modeling and assessing ozone depletion.

The project will also have impact in plasma technology and mass spectrometry. Firstly, the absolute data will have applications in simulating technological atmospheric pressure plasmas. These have developing applications in surgery and water clusters provide key sites for chemical reactivity in these plasmas. Secondly, the original experimental method to produce controlled beams of mass-selected neutral clusters can have numerous applications beyond the scope of this project. As well as diverse variations of the proposed crossed-beam experiments (e.g. using ultrafast lasers), beams of selected neutral clusters can be applied to initiate controlled chemistry on surfaces and hence develop nanotechnologies. The industrial partnership with Hiden Analytical recognises the potential of this proof-of-concept to stimulate a major new line of experimentation on quadrupole-controlled neutral beams with future commercial opportunities in specialised instrumentation.

Publications

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Barc B (2014) Multi-photon and electron impact ionisation studies of reactivity in adenine-water clusters in International Journal of Mass Spectrometry

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Poully JC (2015) Formation and Fragmentation of Protonated Molecules after Ionization of Amino Acid and Lactic Acid Clusters by Collision with Ions in the Gas Phase. in Chemphyschem : a European journal of chemical physics and physical chemistry

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Ryszka M (2016) Dissociative multi-photon ionization of isolated uracil and uracil-adenine complexes in International Journal of Mass Spectrometry

 
Description Electron attachment (EA) plays an important role in radiation chemistry, for example in DNA damage and ozone depletion. Detailed understanding and quantification of EA processes in isolated molecules and condensed environments is therefore essential to model radiation effects on the nanoscale. My EPSRC CAF probes EA resonances and reactive pathways in Stark-selected biomolecular clusters, building on recent advances such as the observation of electron driven proton transfer in Watson Crick pairs [Bowen et al. ChemPhysChem 11 (2010) 880]. However, relatively little is known about how clustering modifies EA absolute cross sections. While theoretical calculations by my collaborators Fabrikant and Gorfinkiel [J. Chem. Phys. 136 (2012) 184301] have provided evidence for strong enhancements in specific cluster configurations, experimental cross sections for EA to clusters are extremely rare. This project is centered on developing an original technique to produce neutral mass-selected beams with known target density for EA experiments. The method involves neutralization of quadrupole-selected cluster anions by electron photo-detachment from specific weakly-bound anionic states, with minimal change in stability and hence dissociation. The project will provide a breakthrough in quantifying the effects of the local chemical environment on electron attachment processes.
The funded period of the project finished in July 2015. The anion selection part of the experiment has been tested and has been exploited to investigate the production and stabilities of nitromethane cluster cations and anions. The laser neutralisation part of the experiment has also been designed (based on extensive simulations), constructed, and tested. The combined experiment has been assembled and optimization work in progress. Complementary experiments (multi-photon ionization and electron impact experiments) have been carried out within the framework of the project on some of the target systems that we intend study with the new experiment in the near future (notably hydrated DNA bases). This has led to six publications in international journals as well as a number of conference outputs.
Exploitation Route The project has produced a unique experimental facility that is expected to deliver advances linked to the EPSRC's grand challenges: Understanding the Physics of Life and Novel treatment and therapeutic technologies. This will particularly relate to developments in simulating radiation damage and nano-scale dosimetry in aqueous environments with applications in radiotherapy treatment planning. Notwithstanding the recognized role of dissociative electron attachment in radiation damage to DNA17 (both direct damage and through DEA to water molecules producing local OH radicals), low-energy electron interactions are not accounted for in radiotherapy treatment planning. Advancing the efficacy of cancer therapy methods is essential in view of the UK's aging population and the resultant increasing pressure on the healthcare system. Moreover, computing power no longer prohibits the practical applications of the most accurate Monte Carlo simulations incorporating these effects. Therefore, the development of optimized radiation track simulations applying the most reliable EA and DEA cross sections possible will have real benefits for society. The absolute cross sections for water clusters measured using the new facility will be integrated into Garcia's simulations [Garcia et al. IJMS 277 (2008) 175] (LEPTS, currently based on gas-phase cross sections) as part of a new strategy to account for the hydrogen-bonded environment. Garcia has strong connections with oncologists who are currently carrying out trials comparing clinical radiotherapy treatment plans with damage distributions derived using LEPTS.

Furthermore, data recorded using the new experiment will impact on society through its contribution to understanding environmental chemistries. The small neutral and charged water clusters studied in this project (including nitromethane) are prevalent in the atmosphere. Furthermore, they can provide model systems to help us understand processes in larger clusters, ice crystals, and droplets. Evidently the diverse phases of water play key roles in atmospheric dynamical processes and simulations of their interactions with low energy electrons (the most abundant secondary products of ionizing radiation) require absolute cross sections. Currently available experimental cross sections for electron attachment to selected water clusters are limited to non-dissociative electron attachment. Absolute experimental data is not available for DEA to any doped water clusters. Our choices of doped cluster targets (hydrated CF3Cl) are partially motivated by the suitability of these species for Gorfinkiel and Fabrikant's calculations [Fabrikant, Gorfinkiel et al. J. Chem. Phys. 136 (2012) 184301] and partially by their role in ozone depletion chemistries in polar stratospheric clouds [Tachikawa et al. PCCP 10 (2008) 2200]. While the specific complexes studied in this project are not expected to have a significant presence in these environments, they can have a major impact on the residence time of CF3Cl at lower altitudes and hence on the molecule's transport to polar stratospheric clouds. Enhanced DEA cross sections for CF3Cl in hydrated clusters can therefore have significant implications for modeling ozone depletion.
Sectors Chemicals,Environment,Healthcare

URL http://physics.open.ac.uk/clusters/electron.php
 
Description This project has produced a unique experimental system with the capability of measuring absolute cross sections for electron attachment to molecular clusters. Some aspects of the experimental functionality (notably cluster anion selection) have already been demonstrated and exploited to provide new data. Other aspects (notably the selective neutralisation by laser photo-detachment) are at an advanced stage but optimization work is on going. We aim to produce new absolute data for radiation damage simulations in the next 12 months. The project has so-far led to 10 publications in international journals as well as a number of conference contributions.
First Year Of Impact 2013
 
Description GANIL 
Organisation Large National Heavy Ion Accelerator
Country France 
Sector Academic/University 
PI Contribution This collaboration is centred on our common aim of understanding of radiation physics and chemistry at the molecular scale, with an emphasis on the effect of nanohydration. The main strength and novelty of our experimental approaches lies in the selection and control of the molecular systems under study. My group at the OU are exploiting a Stark deflection system to control neutral molecules and clusters (EP/J002577/1). We are also developing a complementary system based on cluster anion selection and subsequent neutralisation (EP/L002191/1). We probe radiation effects in multi-photon ionization, electron impact ionization, and electron attachment experiments.
Collaborator Contribution We are able to investigate only relatively small systems at the Open University, whereas larger molecules such as proteins can be brought into the gas phase by electrospray ionization sources. Our collaborators in Caen (notably Poully and Vizcaino) are building an experiment to enable the study of ion collisions with trapped ionic molecules and clusters. While suitable for the study of small systems, will enable the selection and irradiation of systems that are closer to a biologically relevant target (macromolecules and large clusters).
Impact This collaboration has so-far yielded two papers, with one more currently at an advanced stage of preparation. Furthermore, we have applied for a collaborative grant to support exchanges between the two laboratories (CNRS International Programs For Scientific Cooperation). Our proposal has been selected for funding, pending security verification. Publications based on this collaboration: 1. Formation and fragmentation of protonated molecules after ionization of amino acid and lactic acid clusters by collision with ions in the gas phase J-C. Poully, V. Vizcaino, L. Schwob, R. Delaunay, J. Kocisek, S. Eden, J-Y. Chesnel, A. Mery, J. Rangama, L. Adoui, and B.A. Huber ChemPhysChem 16 (2015) 2389 2. Multi-photon and electron impact ionisation studies of reactivity in adenine-water clusters B. Barc, M. Ryszka, J.-C. Poully, E. Jabbour Al Maalouf, Z. el Otell, J. Tabet, R. Parajuli, P.J.M. van der Burgt, P. Limão-Vieira, P. Cahillane, M. Dampc, N.J. Mason, S. Eden Int. J. Mass. Spectrom. 365-366 (2014) 194
Start Year 2013
 
Description Heriot Watt University 
Organisation Heriot-Watt University
Department Physics
Country United Kingdom 
Sector Academic/University 
PI Contribution We have collaborated with Townsend and co-workers at Heriot-Watt University, culminating in the experiments, analysis, and interpretations in the paper below. Most of the experiments in the paper were performed by Townsend and co-workers in their lab at Heriot Watt, albeit with some assistance from a visiting student from my group. My most important contribution to the work was to initiate the collaboration in order to tackle a specific research question: could Townsend's ultrafast pump-probe spectroscopy be used to probe a ring-opening conical intersection in uracil that had been suggested by our experiments at the OU (as part of this ESPRC fellowship)? We also contributed new results to the paper from the OU in order to enable the most direct comparison possible with Townsend's experiments. Since completing the work above, we have extended the collaboration by building two new laser-thermal-desorption sources at the OU. This equipment was inspired by Townsend's methods and he has advised their design. We are currently preparing a collaborative paper that presents new multi-photon ionisation experiments at the OU on the nucleoside uridine.
Collaborator Contribution As noted above, most of the experiments that have been published from this collaboration so far were performed by Townsend and co-workers at Heriot Watt. As Townsend's group evidently has the most relevant expertise in ultrafast spectroscopies, they also led on the analysis, interpretations, and drafting for this paper. The subsequent experiments in the collaboration have been performed by my group and co-workers with design advice from Townsend.
Impact Ultraviolet relaxation dynamics in uracil: time-resolved photoion yield studies using a laser-based thermal desorption source O. Ghafur, S. Crane, M. Ryszka, J. Bockova, A. Rebelo, L. Saalbach, S. De Camillis, J. Greenwood, S. Eden, D. Townsend J. Chem. Phys. 149 (2018) 034301 - featured article with JCP press release (17/07/2018)
Start Year 2016
 
Description Hiden Analytical 
Organisation Hiden Analytical Ltd
Country United Kingdom 
Sector Private 
PI Contribution The experimental design at the heat of my EP/L002191/1 project combines a cluster anion source with a quadrupole assembly, an RF supply, and a laser to produce controlled beams of mass-selected neutral clusters for collision experiments. We will use this system to perform electron attachment experiments on molecular clusters, providing a test for theoretical calculations and absolute data for simulations.
Collaborator Contribution Hiden Analytical have two roles in the project. Firstly, they advise the group on design issues and have produced essential hardware for the experiment: the quadrupole assembly and the RF power supply system. Secondly, they have sponsored a PhD studentship associated with the project. The total value of the sponsorship will be £6,000 for laboratory consumables and the student's travel to attend conferences. They have also offered the student the opportunity to gain work experience at Hiden Analytical, contributing to his training and awareness of potential collaborations between Universities and commercial R&D.
Impact There are no outputs yet in terms of publications and experimental proof of principle as we are still building the apparatus. However, the sponsorship has enabled the students in my group to attend several international conferences, with general associated cultural benefits.
Start Year 2013
 
Description University of Nebraska 
Organisation University of Nebraska–Lincoln
Country United States 
Sector Academic/University 
PI Contribution This partnership extends Ilya Fabrikant's existing collaboration with my co-worker at the OU, Jimena Gorfinkiel. Gorfinkiel and Fabrikant are developing original theoretical approaches combining ab initio (R-matrix) treatments with methods to incorporate nuclear motion in limited degrees of freedom in order to simulate inelastic electron-cluster interactions, including dissociative electron attachment. My two current EPSRC projects are centred on measuring the changes in the resonant energies of electron attachment processes due to clustering (EP/J002577/1) and measuring absolute cross sections for electron attachment to mass-selected clusters (EP/L002191/1). Comparing our data with their calculations will test Gorfinkiel and Fabrikant's developing methodologies and provide new insights into the fundamental mechanisms.
Collaborator Contribution In parallel with the experiments providing a test for the theory, the theoretical work will be key for the interpretation of the experimental data.
Impact The experiment is currently being optimised. Results are expected in the near future that will enable our first comparisons with theory. As electron attachment processes are known to play an important role in radiation-induced damage to biological material, the results will provide new insights into the effects of hydrogen bonding on the radio-sensitivity of specific important biomolecules (notably DNA bases and related biomolecules). This can have societal impact because the new insights and data can lead to improvements in molecular-scale Monte Carlo models of radiation effects in biological material and thus guide radiotherapy innovations. Ilya Fabrikant, Nigel Mason, Juraj Fedor, and I are currently preparing an invited review entitled Recent Progress in Dissociative Electron Attachment: from Diatomics to Biomolecules (Advances In Atomic, Molecular And Optical Physics).
Start Year 2011